In general, a clamp of a die casting machine or injection molding machine is structured arranging a fixed platen supporting a fixed die or mold and a moving platen supporting a moving die or mold on a base plate, fixing ends of tiebars (usually four) passing through the moving platen at the fixed platen, and making the moving platen advance and retract along the tiebars to and from the fixed platen to open/close the die or mold and produce cast articles or molded articles.
In casting (or die casting) or injection molding using the above clamp, the work of changing the mold or die becomes necessary due to a change in the cast article or molded article, wear of the mold or die, etc., but at the time of the changing work, the presence of the tiebars sometimes obstructs the mold or die changing work, so to secure work safely and ease, usually a structure is employed pulling out the tiebars from the fixed platen to the moving platen side (see, for example, Japanese Patent Publication (A) No. 8-72113, Japanese Patent Publication (A) No. 9-57803, Japanese Patent Publication (A) No. 2000-52353, Japanese Patent Publication (A) No. 2005-144802, and Japanese Patent Publication (A) No. 2006-880).
FIG. 1 shows one aspect of a conventional clamp (see Japanese Patent Publication (A) No. 2005-144802). On a base plate 1, a fixed platen 2 supporting a fixed mold 3 is fixed. Further, a moving platen 4 supporting a moving mold 5 is arranged to be able to advance and retract to and from the fixed platen 2 through slide shoes 6.
Further, front ends of tiebars 10 passing through insertion holes 7 and 8 provided at the four corners of the fixed platen 2 and moving platen 4 are detachably fastened to the fixed platen 2 by first fasteners 11 (boxes 14 in which openable split nuts 15 engaging with threads 13 are arranged).
Further, the middle parts of the tiebars 10 are detachably fastened to the moving platen 4 by second fasteners 12 (boxes 17 in which openable split nuts 18 engaging with multiple straight grooves 16 are arranged).
The moving platen 4 has oil hydraulic cylinders 20 mounted on it corresponding to the positions of arrangement of the tiebars 10. Further, the front ends of the rods 20a of the upper oil hydraulic cylinders 20A mounted on the moving platen 4 are coupled through coupling members 21 to the other ends of the upper tiebars 10, while the front ends of the rods 20b of the lower oil hydraulic cylinders 20B mounted at the bottom of the moving platen 4 (partially housed in the slide shoes 6) are coupled through the coupling members 21 to the other ends of the lower tiebars 10.
In the state using the first fasteners 11 to maintain the fastened states of the tiebars 10 and releasing the fastened states of the tiebars 10 by the second fasteners 12, if operating the oil hydraulic cylinders 20 (upper oil hydraulic cylinders 20A and lower oil hydraulic cylinders 20B) to extend and retract, since the tiebars 10 are fastened, the moving platen 4 can advance and retract to and from the fixed platen 2 to open/close the mold.
When changing the fixed mold 3 and moving mold 5, in the open state, the fastened states of the tiebars 10 by the first fasteners 11 are released, then the upper oil hydraulic cylinders 20A are made to extend to the maximum extent. The lower oil hydraulic cylinders 20B are used to fix the position of the moving platen 4, so the above operation of the upper oil hydraulic cylinders 20A causes the upper tiebars 10 to retract and open the top of the part between the fixed platen 2 and moving platen 4 to form a work space enabling mold changing work to be performed without obstruction.
In this way, a conventional clamp employs a structure pulling out the tiebars 10 to the rear of the moving platen at the time of changing molds, so when installing a clamp in a factory, it is necessary to provide sufficient tiebar retraction space behind the moving platen.
However, the tiebar retraction space, as explained above, is a space prepared for just enabling retraction of the tiebars at the time of changing molds. While the clamp is working, it is a completely unused space. Furthermore, when the tiebars have retracted, it is necessary to avoid breakage or damage to the tiebars due to collision or contact with other equipment, apparatuses, etc., so it is necessary to avoid arranging other equipment and apparatuses in the tiebar retraction space.
If the clamp is made large in size, the tiebar retraction space also must be made large along with this, but securing a larger tiebar retraction space used only when changing the molds in the limited installation space is itself not preferable from the viewpoint of the efficient utilization of the installation space.
Further, if the tiebar retraction space is large in the limited installation space, the space for arranging various equipment required for control of the clamp inevitably becomes narrower. This creates a situation making it necessary to densely arrange various control equipment in a narrow space, which degrades the work environment, and makes maintenance and inspection work of the control equipment difficult.
The illustrated patent documents disclose technology for pulling out tiebars in clamps, but all of these employ structures predicated on structures pulling out the tiebars from the fixed platen sides to the rear of the moving platen sides at the time of changing molds, so when installing the above clamps in factories, it is necessary to provide sufficient tiebar retraction space behind the moving platens.
That is, in the structures of conventional clamps, no means or improvements are being made from the viewpoint of the effective utilization of the installation space.